Shadow mask and overscan shield assembly

ABSTRACT

An improved shadow mask and overscan shield assembly for a color cathode ray tube has a metallic generally rectangular shaped mask supporting frame having a peripherally continuous substantially constant cross-section. The frame has a ring portion extending transversely with respect to the cathode ray tube center axis and a flange portion substantially parallel to the axis. A spherically curved color selection mask having an extended skirt of varying width is secured to the flange portion of the frame. An electron shield secured to the ring portion of the frame has a curved outwardly extending portion which bridges the gap between the frame and the inner wall of the color cathode ray tube envelope to shield the screen from impingement by electrons deflected from the side walls of the envelope and also has an inwardly extending portion of curviform rectangular outline to define the electron beam scansion limits of the screen.

Unite .1%.

Mac Lean et a1.

States atent [1'91 [451 Feb. 25, 1975 SHADOW MASK AND OVERSCAN SHIELDASSEMBLY [75] Inventors: Gerald K. Mac Lean, Hoffman Estates; Thomas C.Minzenberger, Lake Bluff, both of 111.

[73] Assignee: Zenith Radio Corporation, Chicago,

[22] Filed: Sept. 10, 1973 [21] App]. No.: 395,893

Related US. Application Data [63] Continuation of Ser, No. 204,241, Dec.2, 1971,

abandoned.

[52] US Cl. 313/407, 313/408 [51] Int. Cl. H01j 29/06, l-l0lj 29/08,l-lOlj 31/20 [58] Field of Search 313/855 [56] References Cited UNITEDSTATES PATENTS 3,349,272 10/1967 Bathelt et al. 313/85 S 3,404,30310/1968 Levin 313/85 5 3,454,813 7/1969 Lewinson 313/85 S 3,473,06510/1969 Schwartz et al. 313/85 S 3,506,867 4/1970 Kraner l 313/85 S3,585,431 6/1971 Long 313/85 S J. OConnor; Nicholas A. Camasto [57]ABSTRACT An improved shadow mask and overscan shield assembly for acolor cathode ray tube has a metallic generally rectangular shaped masksupporting frame having a peripherally continuous substantially constantcrosssection. The frame has a ring portion extending transversely withrespect to the cathode ray tube center axis and a flange portionsubstantially parallel to the axis. A spherically curved color selectionmask having an extended skirt of varying width is secured to the flangeportion of the frame. An electron shield secured to the ring portion ofthe frame has a curved outwardly extending portion which bridges the gapbetween the frame and the inner wall of the color cathode ray tubeenvelope to shield the screen from impingement by electrons deflectedfrom the side walls of the envelope and also has an inwardly extendingportion of curviform rectangular outline to define the electron beamscansion limits of the screen.

1 Claim, 4 Drawing Figures RELATED APPLICATION This application is acontinuation of application Ser. No. 204,241, filed Dec. 2, 1971, andnow abandoned.

BACKGROUND OF THE INVENTION The invention pertains to picture tubes ofthe type used in television receivers, and more particularly to animproved shadow mask and overscan shield assembly for color televisionpicture tubes.

In color picture tubes of the kind with which the invention isconcerned, it is common to provide an evacuated envelope of glasscomprising a screen panel section sealed to a mating funnel section. Atone end of the funnel there is a neck which houses an electrodearrangement forming one or more electron guns for projecting a stream orstreams of electrons toward the screen positioned at the other end. Asin the case of a black-and-white picture tube, the energy of theelectrons approaching the screen is converted into light by a suitablephosphor, which may be coated on the inside surface of the screen. Thecolor tube, in one practical form of embodiment, utilizes a phosphorscreen which is differentiated from point-to-point in that differentadjacent elemental areas of the screen are of different phosphormaterials to produce light of different colors. A parallax barrier,formed usually of very thin metal capable of interrupting the electronstream, is disposed adjacent the phosphor screen on the gun side, andthis barrier is perforated with a large number of aperturesgeometrically related to the elemental phosphor areas producing thedifferent colors oflight. The geometrical relationship is such that bycontrolling the beam direction, phosphor areas of differentcolor-producing quality can be selectively energized to produce avisible picture corresponding faithfully to the composition of theoriginal scene.

In prior art tubes having a spherically shaped shadow mask, the leadingedge of the support frame is contoured in a fashion corresponding to itsintersection with the spherical mask. Thus it is of scallopedconfiguration, being wider in the center portions of each side andnarrower at the corners. The prior art supporting frame also has a ringportion perpendicular to the flange which determines the extent to whichthe tube screen is scanned by the electron beam or beams and also is ofnon-constant dimension. It is dimensioned in such a way that its openingresembles an hour-glass configuration to prevent electrons from strikingthe supporting frame flange and indiscriminately impringing upon thescreen. This function performed by the supporting frame ring is commonlyknown as the rear window function.

The prior art shadow mask assembly also has an electron shield securedto the ring portion of the supporting frame. The supporting frame issecured to the inner walls of the screen section of the cathode ray tubebut is spaced apart therefrom. The electron shield is provided to bridgethe gap between the inner wall of the envelope and the outer dimensionof the intermediate support frame. The electron shield is normally of avery thin metal, such as cold rolled steel foil.

While the prior art shadow mask assembly, as previously described, hasbeen generally effective, it has had the fault of being relativelyheavy, adding excessive weight to the picture tube. Excessive tub'eweight creates handling difficulties during the transit of these cathoderay tubes, even though the tubes may be packaged in protective cartons.It has been found that even small reductions in cathode ray tube weightresults in substantially less breakage.

Also, since the skirt portion of the mask is relatively narrow indimension, any weld placed along this skirt "portion to secure the maskto its supporting frame transmits a stress in the direction of the maskcausing mask deformations in the peripheral areas of the mask. Thiscauses degradation of the tube performance which is especiallynoticeable in the purity of the displayed image.

Accordingly, it is an object of the present invention to provide animproved shadow mask assembly for a color cathode ray tube.

It is a further object of the invention to provide a shadow maskassembly for a color cathode ray tube which is lighter in weight thanprior structures.

It is a more specific object of the invention to provide a shadow maskassembly where the welding stresses applied to the mask are diminishedso that improved color purity may be obtained in a tube incorporatingsuch an assembly.

SUMMARY OF THE INVENTION The invention provides an improved shadow maskand overscan shield assembly for a color cathode ray tube of the typehaving a glass envelope comprising a curved generally rectangular imagescreen panel section and a mating funnel and neck section thereto, aninterlaced pattern of different phosphors disposed on the curved screensurface, and electron gun means for developing at least one electronbeam for generating a raster upon the screen. The improved shadow maskassembly has a metal generally rectangular-shaped mask supporting framehaving a peripherally continuous substantially constant cross-sectionand symmetrically disposed about the central axis of the envelope. Theframe has a ring portion extending transversely with respect to the axisand a flange portion substantially parallel to the axis, the frame beingattached to the inner wall of the envelope but spaced therefrom. Theleading edge of the flange portion is spaced from the screen surface anddisposed in a single flat plane perpendicular to the tube axis. A metalshadow mask, of thinner metal stock than the frame, has amulti-apertured parallax barrier with a curvature generally conformingto that of the curved screen surface and with its apertures in spacedpredetermined registration with the phosphor pattern and having anintegral skirt extending from the parallax barrier parallel to the tubeaxis into surface contact with the flange portion of the frame andsecured thereto. A metal foil electron shield secured to the ringportion of the frame has a curved outwardly extending portion whichbridges the gap between the frame and the inner wall of the envelope anda second portion extending inwardly from the frame toward the tube axisto constitute a curviform rectangular rear window with inwardly curvedsides for intercepting overscan electrons and preventing theirimpingement upon the flange portion of the frame, the shadow mask skirt,or the inner side walls of the envelope.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the present inventionwhich are be- FIG. 1 is a side view, partly in section, of a shadow masktype of color cathode ray tube embodying a shadow mask assemblyconstructed in accordance with the invention;

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a fragmentary cross-sectional view, partially cut away, takenalong line 3-3 of FIG. 2; and

FIG. 4 is a fragmentary cross-sectional view, partially cut away, takenalong line 4-4 of FIG. 3.

Referring now more particularly to FIG. 1, the color cathode ray tubethere represented has an envelope comprising a curved generallyrectangular image screen panel section and a funnel and neck section 11.Envelope sections 10 and 11 are matched as to configuration anddimension and integrated by the usual frit seal 12. The curved screensurface of panel 10 bears an interlaced pattern 13 of differentphosphors, as for example a multiplicity of dot triads. Each triadconsists of a dot of red phosphor, one of blue and one of green.Customarily the phosphor screen is backed by a layer of conductive lightreflecting material, such as aluminum, of such thickness as to bereadily penetrated by the electrons of the electron beams of the tube.For convenience, the aluminized layer has not been detailed in thedrawing.

At the other end, the tube has the usual base 14 which accommodates thenecessary pins through which connections are conveniently made to theelectrode systems of the tube. These systems comprise a gun mount shownschematically at 15, because the specific construction is of noparticular concern to the present invention. Suffice it to say that thegun mount may be a conventional delta array of three electron gunswhich, when energized, develop three electron beams for scanningphosphor screen 13.

In order to obtain color selection, a multi-apertured parallax barrier16, with a curvature generally conforming to that of the curved screensurface and with its apertures in spaced predetermined registration withthe phosphor pattern, is disposed across the beam path of the tubebetween screen 13 and gun mount 15. Its function, as well understood inthe art, is to achieve color selection by permitting each of the threebeams issuing from the gun mount to see or impinge solely upon anassigned one of the different color phosphor materials of screen 13.Normally, assigned ones of the guns, which are conventionally designatedas red, blue and green guns, energize only the assigned color phosphorcomponent of the screen. The color-selection electrode is supported inposition by mask supporting frame 17 which is also generallyrectangular-shaped. The mask frame 17 is removably secured within thetube envelope by studs 18 projecting inwardly from the envelope toreceive a plurality of mounlng springs 19 carried on the periphery ofthe mask frame 17.

The shadow mask and overscan shield assembly of the present inventioncomprises mask supporting frame 17 which has a peripherally continuous,substantially constant cross-section and is symmetrically disposed aboutthe central axis 21 of the tube envelope. As best seen in FIG. 3, masksupporting frame 17 has a flange portion 17a which is substantiallyparallel to axis 21 and has a leading edge spaced from the curved screensurface of panel section 10 and disposed in a single flat planeperpendicular to axis 21. Frame 17 also has a ring portion 17b whichextends inwardly from flange por tion 17a toward axis 21 and ispreferably perpendicular to the tube axis. In the preferred constructionshown in the drawings, the width of ring portion 17b is substantiallyequal to that of flange portion 17a.

Shadow mask 16, which is formed of much thinner metal stock than frame17 (typically 6 mils sheet steel as compared with mils cold rolled steelfor the frame), comprises a multi-apertured parallax barrier 16a and anintegral skirt 16b extending from the para]- lax barrier parallel totube axis 21 into surface contact with flange portion 17a of the frame,as is best shown in FIG. 3. Parallax barrier 17a has a curvaturegenerally conforming with the curved screen surface and is disposed withits apertures in spaced, predetermined registration with the phosphorpattern of the image screen as is well understood in the art. Skirt 16bis secured, preferably by spot welding at spaced intervals as shown at23 in FIG. 3, to flange portion 17a of frame 17.

Incorporated onto the flange portion of the shadow mask frame areresilient mounting springs 19 which secure the mask assembly within theenvelope in substantially spaced parallel relation to the faceplate byengaging the mounting studs 18. Springs 19 are welded to frame 17 asshown at 26 in FIG. 4. A three-point arrangement has been illustrated inFIG. 1 with the mounting springs on opposing side portions of shadowmask support frame 17 and a mounting spring centrally located at the topof the frame. As can be seen in FIGS. 1, 3 and 4, the periphery ofshadow mask support frame 17 is spaced apart from the inner wall of thefaceplate panel section resulting in a space therebetween.

A metal foil electron shield member 20 is provided in surface contactwith ring portion 17b of frame 17, and shield member 20 is secured toring portion 17b, preferably by spot welding at spaced intervals, asshown at 22 in FIGS. 2 and 4. Shield member 20 has a curved, outwardlyextending portion 20a which bridges the gap between frame 17 and theinner side walls of the tube envelope, in a manner which is wellunderstood in the art and which for example may correspond to thatdescribed in detail in U.S. Pat. No. 3,506,867, issued by James Kranerand assigned to the same assignee as the present application. Shieldmember 20 may be formed of a stainless steel foil of 3 mils thickness.

Further in accordance with the invention, metal foil shield member 20includes a second portion 20b which extends inwardly beyond the inneredge of ring portion 17b of frame 17 toward the tube axis 21 toconstitute a curviform rectangular rear window with inwardly curvedsides as best illustrated in FIG. 2. The inwardly extending portion 20bof shield member 20 intercepts overscanned electrons from the gunassembly and prevents them from impinging upon and scattering from theinner surface of flange portion 17a of the frame or upon skirt 16b ofthe shadow mask, while the curved outwardly extending portion 20aprevents overscanned electrons from passing between the shadow maskassembly and the envelope to the phosphor screen.

The shadow mask and overscan shield assembly of the present inventionprovides distinct and important advantages with respect to prior artconstructions. Firstly, the mask supporting frame 17 is of much simplerconstruction and lighter weight than the support frames of previouslyused shadow mask assemblies. Secondly, because the shadow mask skirt iswelded to the supporting frame at locations which are removed from thecurved parallax barrier portion of the mask, there is a greatly reducedlikelihood of deforming the parallax barrier during assembly of the maskto the frame. Because of the greater simplicity in construction and thehigher yield or lower reject rate attributable to the improved ease ofassembling the mask to the frame without injury to or deformation of theapertured parallax barrier, the construction of the present invention issignificantly more economical than previously used constructions. Andthese advantages are obtained without sacrificing structural strength orstability as compared with prior constructions using scallopedsupporting frames of comparable cross-section in the corners but heavieron the sides.

While a particular embodiment of the invention has been shown anddescribed, modifications may be made, and it is intended in the appendedclaims to cover all such modifications as may fall within the truespirit and scope of the invention.

We claim:

1. in a color television picture tube of the type having a glassenvelope comprising a curved generally rectangular image screen panelsection and a mating funnel and neck section sealed thereto, aninterlaced pattern of different phosphors on the curved screen surfaceof said panel section, and electron gun means housed in said funnel andneck section for scanning the phosphors on said curved screen surfacewith electrons, an improved shadow mask and overscan shield assemblycomprising:

a metal generally rectangular mask supporting frame having aperipherally continuous substantially constant cross-section andsymmetrically disposed about the central axis of said envelope, saidframe having a flange portion substantially parallel to said axis with aleading edge spaced from said screen surface and disposed in a singleflat plane perpendicular to said axis and a ring portion, of a widthsubstantially equal to that of said flange portion, extending inwardlyfrom said flange portion toward said axis and substantiallyperpendicular thereto, and said frame being secured to said envelopewith a space between said frame and the inner side walls of saidenvelope;

a metal shadow mask, of thinner metal stock than said frame, having amulti-apertured parallax barrier with a curvature generally conformingto that of said curved screen surface and with its apertures in spacedpredetermined registration with said phosphor pattern and having anintegral skirt extending from said parallax barrier parallel to saidaxis into surface contact with said flange portion of said frame andsecured thereto;

and a metal foil electron shield member in surface contact with saidring portion of said frame and secured thereto, having a curvedoutwardly extending portion bridging the gap between said frame and saidenvelope side walls and a second portion extending inwardly from saidframe toward said axis to constitute a curviform rectangular rear windowwith inwardly curved sides, for intercepting overscan electrons fromsaid electron gun means and preventing their impingement upon the flangeportion of the mask frame, the shadow mask skirt,

or the inner side walls of the envelope.

1. In a color television picture tube of the type having a glassenvelope comprising a curved generally rectangular image screen panelsection and a mating funnel and neck section sealed thereto, aninterlaced pattern of different phosphors on the curved screen surfaceof said panel section, and electron gun means housed in said funnel andneck section for scanning the phosphors on said curved screen surfacewith electrons, an improved shadow mask and overscan shield assemblycomprising: a metal generally rectangular mask supporting frame having aperipherally continuous substantially constant cross-section andsymmetrically disposed about the central axis of said envelope, saidframe having a flange portion substantially parallel to said axis with aleading edge spaced from said screen surface and disposed in a singleflat plane perpendicular to said axis and a ring portion, of a widthsubstantially equal to that of said flange portion, extending inwardlyfrom said flange portion toward said axis and substantiallyperpendicular thereto, and said frame being secured to said envelopewith a space between said frame and the inner side walls of saidenvelope; a metal shadow mask, of thinner metal stock than said frame,having a multi-apertured parallax barrier with a curvature generallyconforming to that of said curved screen surface and with its aperturesin spaced predetermined registration with said phosphor pattern andhaving an integral skirt extending from said parallax barrier parallelto said axis into surface contact with said flange portion of said frameand secured thereto; and a metal foil electron shield member in surfacecontact with said ring portion of said frame and secured thereto, havinga curved outwardly extending portion bridging the gap between said frameand said envelope side walls and a second portion extending inwardlyfrom said frame toward said axis to constitute a curviform rectangularrear window with inwardly curved sides, for intercepting overscanelectrons from said electron gun means and preventing their impingementupon the flange portion of the mask frame, the shadow mask skirt, or theinner side walls of the envelope.